Description from
Flora of China
Persicaria japonica (Meisner) H. Gross ex Nakai; ?Polygonum macranthum Meisner; P. martini H. Léveillé & Vaniot; P. myosurus Franchet.
Flowers small. Perianth 3-4 mm, not glandular dotted. Achenes shiny.
Marshy areas, ditches, streamsides; sea level to 1700 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Japan, Korea].